Abstract

Imaging systems using soft X-ray reflective optics can be configured with either a transmission [1] or reflection mask [2] to print onto resist coated wafers. Transmission masks are well suited for high contrast and high resolution imaging. However, thin membranes are needed for such masks which can be fragile and sensitive to heating effects. Ultimately it is therefore desirable to take advantage of the robust nature of a thick reflecting mask. Practical reflective masks intended for use at λ=13 nm require Mo/Si multilayer reflective coatings with minimum features sizes from 2.0 to 0.1 μm in order to demonstrate a 0.1 μm printing capability with systems designed mask to wafer reduction from 20X to 1X, respectively. In this work we compared a variety of technologies for patterning transmissive and reflective masks containing features on this size scale. Transmissive masks which are reported consist of patterned absorbers on silicon membranes with features as small as 0.1 μm. Reflective masks patterned using various methods including; absorbing layers formed on top of multilayer reflectors; reflective coating removal by reactive ion etching (RIE); and ion damage of multilayer regions by ion implantation are also reviewed [2]. With a view to the future,we have begun to assess these reflective masks in a number of areas. Of principal interest are the reflectance contrast; resolution; process complexity; and repairability.

© 1992 Optical Society of America